A turbocharger is a well known means of providing pressurized air to an internal combustion engine. A typical turbocharger features a turbine wheel driven by engine exhaust gases. The turbine drives a compressor that provides pressured air to the combustion engine's intake to increase engine performance. In general, as the speed of the combustion engine increases exhaust gas pressure increases. The turbocharger translates increased exhaust gas pressure into increased intake air pressure (boost pressure) and performance improves within practical limits. However, the uncontrolled pressurization of intake air can lead to problems with engine operation and can result in damage to the engine and turbocharger.
A typical turbocharged engine features a device known as a wastegate that allows exhaust gases to bypass the turbocharger when it is not desirable to increase intake air pressure. One such circumstance is when an increase in boost pressure would result in engine damage. When exhaust gases are diverted away from the exhaust turbine wheel, the turbocharger slows and boost pressure is reduced. A wastegate may divert variable amounts of the exhaust gases in response to a variety of control mechanisms known in the art.
Various devices have been disclosed in the prior art which operate a wastegate valve in response to many parameters. A common control parameter used to regulate the operation of a wastegate is the pressure difference that develops across a throttle valve placed between the turbocharger and an intake manifold of a combustion engine. Many of these systems are directed to particular applications requiring complex control systems such as aircraft engines operating in variable air pressure and temperature environments or high performance automobile engines which typically experience rapid changes in throttle application. Such systems often incorporate complex electronics and arrangements of mechanical elements and require specialized equipment and expertise to maintain.
Alternatively, simpler engines or engines designed to be operated primarily in slowly varying load conditions often use a simplified wastegate design which features a valve controlled by a diaphragm and held shut by a spring. The spring rests on the diaphragm in contact with a pressure space which is maintained at the pre-throttle boost pressure. When boost pressure applied to the diaphragm is sufficient to overcome the spring force, the valve is opened and exhaust gases bypass the turbocharger. This pressure set point may be reached while the throttle is closed or open with the wastegate actuator responding to both engine load conditions in the same manner. The adjustment of the chosen pressure set point is accomplished by adjusting the spring tension of the wastegate actuator. It is often not practical or even possible to adjust the spring tension of the wastegate actuator to account for varying conditions during the operation of the engine using these simplified designs.
Control of the wastegate using a diaphragm does not maintain a pressure differential across the throttle valve of the engine. Engines could benefit from maintaining a pressure differential across the throttle valve; however, the systems used to control the wastegate to maintain the pressure differential are typically too complex to make their use suitable in many engine applications.